BaseTest now ensures that unittest.TestCase.assertWarns() uses the same
warnings module than warnings.catch_warnings(). Otherwise,
warnings.catch_warnings() will be unable to remove the added filter.

when the test is interrupted (or fail).

Mention also the detected GDB version on verbose mode and on error (if the
major version is smaller than 7).

Also fixes error in 'kill' target (already fixed in 2.7, somehow the fix
didn't make it to this branch).

Patch from Mattip.

on Windows and Cygwin.  Patch from Akira Li.

Patch from Berker Peksag.

Patch from Berker Peksag.

Patch by tagatac

Patch by Mark Roseman.